ft_atoi.c

static int		skip_spaces(const char *s, int i)
{
	while (s[i] == ' ' || (9 <= s[i] && s[i] <= 13) || s[i] == '\n')
		++i;
	return (i);
}

int				ft_atoi(const char *str)
{
	int i;
	int n;
	int sign;

	n = 0;
	i = 0;
	sign = 1;
	i = skip_spaces(str, i);
	if (str[i] == '+' || str[i] == '-')
	{
		sign = (str[i] == '+') ? 1 : -1;
		++i;
	}
	while ('0' <= str[i] && str[i] <= '9')
	{
		n = n * 10 + (str[i] - '0');
		++i;
	}
	n = sign * n;
	return (n);
}